Numerical simulations for a quantitative analysis of AFM electrostatic nanopatterning onPMMA by Kelvin force microscopy

Abstract

Electrostatic nanopatterning of electret thin films by atomic force microscopy(AFM) has emerged as an alternative efficient tool for the directed assembly ofnano-objects on surfaces. High-resolution charge imaging of such charge patternscan be performed by AFM-based Kelvin force microscopy (KFM). Nevertheless,quantitative analysis of KFM surface potential mappings is not trivial because ofside-capacitance effects induced by the tip cone and the cantilever of the scanning probe.In this paper, we developed numerical simulations of KFM measurementstaking into account these artifacts, so as to estimate the actual surface chargedensity of square charge patterns (nominal sizes ranging from 100 nm to 10 µm) written by AFM into polymethylmethacrylate (PMMA) thin films. This work revealedthat, under our conditions, such charge patterns exhibit a surface charge density between1.5 × 10 − 3 and3.8 × 10 − 3 C m − 2, depending on the assumed depth of injected charges. These results are crucial to quantifythe actual electric field generated by such charge patterns and thus the electrostatic forcesresponsible for the directed assembly of nano-objects onto these electrostatic traps.